Abstract The focus of this Research Project, originally funded May 1, 1996, renewed June 1, 2002, and renewed again April 1, 2004, has been the role of CpG island hypermethylation changes targeting GSTP1, encoding the p-class glutathione S-transferase, in the pathogenesis of prostate cancer (PCA). Since its inception, Project studies have resulted in 35 peer-reviewed manuscripts (16 since the last competitive renewal) and 19 review articles published, as well as in major new insights into how PCAs likely arise. Specifically, the discovery from this Project that the most common somatic genome alteration yet described for prostate cancer, hypermethylation of the GSTP1 CpG island, appears first in proliferative inflammatory atrophy lesions, prostate cancer precursors that arise in response to inflammatory damage to the prostatic epithelium, has stimulated intense interest in the role of chronic or recurrent inflammation in prostatic carcinogenesis. For the next funding period, the major hypothesis to be addressed is that somatic CpG island hypermethylation changes, at GSTP1 and at other gene loci, arise in an inflammatory milieu as a result of increased expression and/or activity of DNMTs. Provocative preliminary data hint that reactive nitrogen species, elaborated by inflammatory cells, may drive DNA methylation by a direct effect on DNA methyltransferase function. To test this new mechanism, three Specific Aims are proposed: (1) a characterization of post-translational modifications of DNMTs, including S-nitrosation in response to nitric oxide exposure, which promote de novo DNA methylation, (2) an evaluation of genome-wide differences in DNA methylation and chromatin structure in normal and neoplastic prostate cells, and the effects of nitric oxide exposure on patterns of genome DNA methylation, and (3) an assessment of the effects of chronic inflammation on prostatic carcinogenesis in Gstp1/2+/+ versus Gstp1/2-/- mice, and on de novo GSTP1 hypermethylation in Gstp1/2-/-GSTP1+ mice.